How were natural insulation materials hemp, cellulose and cork used in WISE?

There are three main types of insulation in WISE, in the walls, floor, and roof.

Hemp & Lime wall insulation

The external walls in WISE consist of 500mm of a hemp-lime mix, stabilised with 15% cement. The binder used was 'Tradical HB', and was developed for use with hemp. The mix is often known as Hempcrete.

This insulation was applied in a similar way to that of casting concrete, by spraying the material against temporary shuttering, fully enclosing the timber frame in the process and therefore providing a hugh degree of air-tightness whilst remaining breathable. Breathability refers to the ease of passage of moisture through the walls, and is a characteristic of both lime and hemp (but not of concrete or cement).

The addition of the (usually Portland) cement helps to increase the plasticity of the mix when it is applied and also adds flexibility when the structure is set.

In WISE, the hempcrete was sprayed into the shuttering to a thickness of 500mm, completely encasing the timber frame and therefore reducing the chance of thermal bridging. This is then finished with a lime render. These walls have a u value of ~0.14W/m2/K, but also has the added benefits of both storing heat and allowing moisture to travel through the walls.

Cellulose insulation

The roof in WISE is largely insulated using cellulose (recycled paper) insulation. It is advised for use in ventilated or breathing constructions and as such is ideal for WISE, with the natural ventilation and hempcrete walls. Cellulose insulation has a very low embodied energy of 0.94-3.3 MJ/kg; compared to 28 MJ/kg for fiberglass and 88.60 MJ/kg for expanded polystyrene.

Cork insulation

This was used in some of the roofs and in key places in the foundations of WISE, to avoid any cold bridging. Cork also has a low embodied energy of only 4.0 MJ/kg, but also has the benefit of being waterproof and therefore able to be used in situations where other natural insulation materials would not be suitable.

Most cork is from Portugal, Spain or Northern Africa, where the cork oak tree grows. Fortunately, cork can be (and generally is) produced organically as its management does not require the use of any pesticides, fertilisers or irrigation. Hence it has a low environmental impact.